1. Field of the Invention
The present invention relates to an endoprosthesis percutaneously implantable by means of a catheter in the body of a patient, particularly in tubular vessels or organs, said endoprosthesis being designed in the form of an oblong, hollow body and, upon placement in the correct position during implantation, being changeable from a small lumen during insertion into a larger lumen conforming to its functional position.
2. The Prior Art
Prostheses capable of being inserted percutaneously and changeable in their lumen are known. They serve the purpose of opening or widening vascular lumina either by mechanical expansion by means of known balloon catheters from a small to a larger lumen, or such a prosthesis expands by itself after prior compression by spring force prior to the implantation, due to the initial stress produced in the spring during the compression.
EP-A-0,292,587 describes an endoprosthesis that is received on a balloon catheter and expandable by dilation, as well as detachable from the catheter and placed in a vessel. This prosthesis is a "stent" manufactured by knitting or crocheting from metal or plastic thread material into the form of a hose-like hollow body, in connection with which the individual stitches consist of loosely meshing loops. During expansion, widening, due to dilation of the balloon of the catheter, the meshing loops undergo plastic deformation, and the expanded prosthesis thus remains in its expanded position.
Self-expanding stents have been described in the prior art, for example in EP-A-0,183,372, U.S. Pat. No. 4,732,152 and DE-OS 4,137,857. Prior to their implantation, these prostheses are compresses against inherent spring return forces to a reduced cross section, inserted into the body in the compressed state, and, upon placement in the correct position, expand again in the respective vessel or hollow body of the patient's body due to cancellation of the force of retention, and are fixed thereby.
The endoprosthesis described in EP-A-0,183,372 is one which, for the purpose of implantation, is compressed to a reduced cross section and then pushed in the compressed state by means of a pusher through a catheter previously inserted in the vessel, until it is positioned in the right position in the vessel. Such advancing of the prosthesis through the catheter requires a considerable expenditure of force because the displacement is counteracted by high frictional forces.
A woven and elastically designed endoprosthesis has been described earlier in U.S. Pat. No. 4,732,152, which, in the compressed state, is kept together by a double cover, which is closed at the distal end. This cover is pulled back from the folded prosthesis in the same way as a stocking is pulled from the foot of a wearer. For the purpose of avoiding the friction occurring in this process, liquid may be filled in between the two leaves of the cover. However, this system, which seems to be initially suitable due to the reduction of the frictional resistances, is very complicated with respect to handling.
DE-OS 4,137,857 describes a hollow body. This prosthesis is compressed against the action of resetting spring forces to a cross section that is reduced versus the widened functional position, and kept in this position by means of a mountable covering. After the covering has been mounted, the prosthesis automatically widens to a cross section conforming to the functional position. The covering, which may be a meshwork approximately in the form of a round crocheting, extends over the entire length of the prothesis and consists of at least one through-extending filament and one pull-up line. The prosthesis, which is kept in a radially compressed position by the covering, can be advanced, for example on a guide wire, or also rigidly received axially on the end of a probe or catheter.
Finally an endoprosthesis is known, for which no documentation is available in the form of a published reference made from a memory alloy. This endoprosthesis is an oblong hollow body with a jacket that is broken many times and embodied in the way of a stretched metal.
This endoprosthesis automatically widens from a smaller insertion lumen to a larger lumen. However, this endoprosthesis has little flexibility and in any case potentially has the hazard of fatigue fractures when implanted via a joint. Not all of the struts forming the jacket are connected with each other in the corner points, and, in the implanted state, such struts may thus detach themselves from the vascular wall and protrude into such a wall.